Some very encouraging results in biological control of fleas can
be achieved by using insect/arthropod parasitic nematode worms
(Heterorhabditis spp. & Steinernema spp.). These are available
commercially, and some even target the control of fleas specifically.
For more information about these nematodes, check out-
http://ianrwww.unl.edu/ianr/plntpath/nematode/wormhome.htm
If you don't have a web browser, you can email me for details.
Byron Adams
bjadams at crcvms.unl.edu